1. Field of the Invention
The present invention relates to a solid solution semiconductor laser element material consisting of a solid solution semiconductor having the general chemical formulae Ca.sub.1-x Pb.sub.x X (wherein 0&lt;x&lt;0.5, X is at least one element selected from S, Se and Te) and Ca.sub.1-x (Pb.sub.1-y Y.sub.y).sub.x X (wherein 0&lt;x.ltoreq.0.5, 0&lt;y&lt;1, X is at least one element selected from S, Se and Te), oscillating within a wide region of wavelength 0.2-8 .mu.m and being operable in the vicinity of room temperature, and a laser element with the use of this material. An object of the invention is to provide a laser element which is capable of oscillating within a region of wavelength 0.2-8 .mu.m, varying wavelength and being operable in the vicinity of room temperature, particularly a solid solution semiconductor laser element material which can form a laser element which is capable of having a lattice matching type double hetero junction structure or lattice matching type quantum well structure.
2. Description of the Prior Art
The structure of a semiconductor laser element is explained by referring to FIG. 1. FIGS. 1(A), 1(B) and 1(C) show a lattice matching type double hetero junction structure laser element, a lattice matching type quantum well structure laser element and its partly enlarged view, respectively, and a laser beam is emitted from an active layer 2 sandwiched by cladding layers 1, 1 in the arrow direction by flowing a current through electrodes 3, 3.
In the case of the semiconductor, laser element, a laser beam emitted therefrom is faint is different that emitted from the other gas lasers and the like. Accordingly, to increase luminous efficiency of the laser element a complicated structure has been developed which divides an active layer 2 into a barrier layer 4 and a quantum well 5 as shown in FIG. 1(B).
As a task required for the above-described semiconductor laser, it is important to increase an operating temperature and to have good junction between a cladding layer 1 and active layer 2.
Hitherto, as wavelength variable semiconductor laser element materials within a region of wavelength 0.2-8 .mu.m, there have been known Hg.sub.1-x Cd.sub.x Te where 0&lt;x.ltoreq.1 as a II-VI group compound semiconductor and InAs or InSb as a III-V group compound semiconductor and each kind of IV-VI group compound semiconductors. Among them, the IV-VI group compound semiconductor is noted as the most practically usable material from the point of a high operating temperature and large wavelength variation, and Pb.sub.1-x Cd.sub.x S.sub.1-y Se.sub.y or Pb.sub.1-x Eu.sub.x Te.sub.1-y Se.sub.y as a quaternary lead salt solid solution semiconductor has hitherto been known.
A laser element is usually formed with a double hetero junction structure substantially matching lattice constants of an active layer 2, a charge carrier, and a light beam cladding layer, wherein the cladding layer 1 is made Pb.sub.1-x Cd.sub.x S.sub.1-y Se.sub.y or Pb.sub.1-x Eu.sub.x Se.sub.y Te.sub.1-y, and the active layer 2 is made PbS or Pb.sub.1-x 'Eu.sub.x 'Se.sub.y 'Te.sub.1-y ', respectively. Operating temperatures are 200 K and 270 K, respectively, but only attained by pulse oscillation, and if the pulse oscillation becomes continuous oscillation, operating temperatures are further disadvantageously lowered in the continuous oscillation and cannot practically be used.
Generally, in order to increase the operating temperature of the above injection type semiconductor laser, it is desired to form a laser element with a lattice matching type double hetero junction structure or lattice matching type quantum well structure matching each lattice constant of active layer, a charge carrier and beam cladding layer. It is further greatly desired to make an energy gap of the cladding layer 1 larger than that of the active layer 2 and to make its difference sufficient, but in either one of Pb.sub.1-x Cd.sub.x S.sub.1-y Se.sub.y or Pb.sub.1-x Eu.sub.x Se.sub.y Te.sub.1-y, the difference is small, and as a result, an operating temperature is disadvantageously low.
In case of forming a laser element with a lattice-matching type double hetero junction structure or lattice-matching type quantum well structure, it is necessary to make an energy gap of the cladding layer 1 larger than that of the active layer 2, to make its difference large and to form a laser element with joining materials which crystalline structures and lattice constants are substantially the same. In Pb.sub.1-x Cd.sub.x S.sub.1-y Se.sub.y or Pb.sub.1-x Eu.sub.x Se.sub.y Te.sub.1-y of a quaternary solid solution having a rock salt-type crystalline structure, materials having different energy gaps and substantially equal lattice constants can be obtained by controlling a composition x of Cd or Eu and a composition y of Se, respectively, so that a laser element can be formed by joining them.
However, in case of actually manufacturing a laser element, a large solid solution amount of Pb cannot be expected because of limitations such as a manufacturing condition and the like, and a quaternary solid solution is manufactured by a small amount of solid solution at present. Materials pulse oscillated at 200 K and 270 K as described above are understood that compositions x of Cd and Eu in the above-described quaternary solid solution are 0.05 and 0.018, respectively, and that a solid solution amount to Pb is small. Therefore, in case of using them as a beam cladding layer 1, energy gap difference between the cladding layer 1 and the active layer 2 is at most 0.18 (eV) at 300 K and 0.094 (eV) at 241 K, and a laser element having a high operating temperature could not be obtained.
The demand for high-performance laser elements has recently been increased more and more, particularly the development of solid solution semiconductor laser element material operable in the vicinity of room temperature is important. That is, in order to increase the operating temperature of a semiconductor laser, it is an urgent task to obtain a novel solid solution semiconductor having larger energy gap of the cladding layer than that of the active layer and a sufficiently large difference therebetween.